MIAMI – The Boeing 737 MAX continues to soar above the skies with operators around the world and new buyers welcoming the jet.

However, Boeing detected a problem within the jet fuel system in June 2020. As a result, the US Federal Aviation Administration (FAA) recently forced Boeing 737 MAX operators to modify the jet’s fuel system processors following a proposed Airworthiness Directive (AD).

Photo: Max Langley/Airways

Unsafe Refueling

According to Flightglobal and FAA, a B737 Max operator experienced problems within the jet fuel shut-ff system during refueling. Consequently, the FAA has proposed an AD requiring airlines to replace the jet’s fuel system processors.

Boeing already detected the problem in a Special Attention Requirements Bulletin (SARB) issued in June 2020. In that Boeing detailed compulsory procedures for replacing the fuel quantity processor unit (FQPU). Meanwhile, FAA issued the AD on April 2 and discussed that the problem exists within the “automatic shut-off system” on 737 Max 8 and 9.

According to the FAA, if affected operators donot take proper action against the unsafe condition, it may result in an overfill of the right main fuel tank. As a result, spilled fuel on the ground could reach an ignition source, resulting in a ground fire.

Boeing 737 MAX. Photo: Brandon Farris/Airways

Root Cause and Remedies

As FAA detailed in the AD, an airline reported a problem during refueling the jet. Also, it mentioned that the system is capable to automatically close a valve when the tank is full. However, if the automatic shut-off feature fails, the system should generate a flashing warning on the jets’ “refuel panel”, notifying fuel operators about the failure.

Moreover, The agency got the notification that especially during refueling Max’s right-side tank, the system does not work correctly. Specifically, if the automatic shut-off valve fails to close, the system does not indicate a flashing warning.

According to the proposed AD, the failure is caused by “the flashing threshold in the [fuel quantity processor unit] not being set at the correct fuel level.” Therefore, the FAA mandates operators to replace the processor units and perform FQPU software checks. As a result, airlines shall follow compliance steps as detailed in the SARB issued on June 2, 2020.

Featured image:. TUI Boeing 737 MAX 8 test flight. Photo: Brandon Farris/Airways